A gas turbine engine may be fitted with a fan assembly at its intake to thus form a turbofan or fanjet engine. In such an arrangement, the fan is driven by the gas turbine engine and provides compressed air flow to the gas turbine engine, together with a bypass air flow that provides additional thrust.
In other configurations the gas turbine engine may drive a secondary fan assembly via a driveshaft. This secondary fan assembly may then be used to provide a regulated separate airflow to that passing through the gas turbine engine.
In either of the aforementioned arrangements, the fan assembly comprises a rotational array of fan blades disposed around a hub. Typically several fan assemblies are positions in series with one another with a static interstage vane array being interposed therebetween.
The static interstage vane array redirects the air exiting one fan stage so as to be optimally directed towards the following fan array. The interstage vanes typically each comprise a radially oriented centre aerofoil portion having radially inner and outer platforms.
One example of such a typical vane array arrangement is shown in FIG. 1 in which the aerofoil together with the inner and outer platforms is integrally moulded. The mouldings are then assembled into an engine casing as a circumferential array.
One problem with the prior art arrangement of FIG. 1 is that the complexity of the tooling required to integrally mould the vane makes the process expensive.
A further such problem is that the fillet radius at the junction of the aerofoil portion and each of the inner and outer platforms, which is important to the efficient operation of the vane array, is difficult to produce consistently.
In addition, the moulded vane structure has little intrinsic damping. This requires the vane array to be provided with additional componentry to prevent the high vibration levels caused by operation of the gas turbine engine causing high cycle fatigue of the component. One example of such a solution is the use of damping foil on the vane surfaces to provide damping and so increase fatigue resistance.